Timing and Nature of Wet Climatic Periods in North Africa and in the Arabian Peninsula: Inferences from Isotopic, Chronologic, and Remote sensing data

Abstract:

The wet climatic periods in the Quaternary in north Africa and in Arabia were traditionally attributed to intensification of paleo-monsoons during interglacial periods and progressive northward migration of monsoonal front. In N Africa, the monsoonal model could not account for: (1) progressive W to E depletion (Morocco: -20 to -40‰; ; Libya: -70 to -80‰; Egypt: -80 to -83‰) in isotopic composition of fossil groundwater ; (2) observed high lake levels during glacial periods (e.g., Lake Lisan: 160 m bmsl during glacial period MIS2); (3) the depleted isotopic compositions in the groundwater compared to modern precipitation (e.g., d²H: Morocco: - 25.8‰; ; Libya: -17.7; Egypt: -11.7‰) is consistent with deposition during relatively cool periods; (4) ages (Cl-36 : 170ka to 1000ka) of groundwater in the Empty Quarter are consistent with deposition in glacial periods; and (5) low recharge temperatures (e.g., 2-6 °C below average annual temperatures). Intensification of the paleo-westerlies during previous glacial periods can account for these observations. We propose a similar model for northern and central Arabia and probably the northern sectors of the Empty Quarter. Our reasoning: (1) a progressive north to south depletion in groundwater composition (north & center: d²H :-26.6 to -2.5‰, south: d²H: -76.6 to -26.9‰) is inconsistent with a paleo-monsoon origin; (2) ages of sediments in paleo-lakes (e.g., lake Mundafan: OSL ages: 88 to 147ka) favor deposition during glacial periods; (3) depleted isotopic compositions in the groundwater (d²H: -76.6 to -26.9‰) compared to modern precipitation (d²H: -22 to -45‰); (4) Cl-36 ages of groundwater (170ka to 1000ka ) are consistent with precipitation during glacial periods; (5) well documented records of monsoon-related wet events in Oman are not well developed northwards; and (6) well developed paleo-channels and theater-headed valleys in north and central Arabia compared to southern Arabia.